Pulsed laser

Abstract

A pulsed laser comprises an oscillator (10), a laser medium (14), a wavelength selective member (12) for tuning the wavelength of a beam pulse (18) emitted by the oscillator, and means for pulsed excitation of the laser medium (14). The laser medium (14) is excited at least twice at consecutive times to generate a single beam pulse (18).

What is claimed is: 
     
       1. A pulsed oscillator comprising: a resonant cavity;   a gain medium located within the cavity;   a wavelength selective member for narrowing the wavelengths of light emitted from the cavity; and   means for exciting said gain medium to generate output pulses of laser light, said excitation means generating at least one seed excitation pulse followed by a primary excitation pulse and wherein the time interval between the seed pulse and the primary pulse is sufficient to allow light generated by the gain medium in response to the seed pulse to reach the wavelength selective member and return to said gain medium whereby the light generated in response to the subsequent primary pulse will have an enhanced spectral purity.   
     
     
       2. An oscillator as recited in claim 1 wherein the intensity of the seed excitation pulse is less than the intensity of the primary excitation pulse. 
     
     
       3. An oscillator as recited in claim 1 wherein the intensity of the seed excitation pulse is between 10 and 25 percent of the intensity of the primary excitation pulse. 
     
     
       4. An oscillator as recited in claim 1 wherein the time interval between the seed excitation pulse and the primary excitation pulse is at least 1.5 times the period for light to traverse the cavity. 
     
     
       5. An oscillator as recited in claim 1 wherein the time interval between the seed excitation pulse and the primary excitation pulse is between two and ten times the period for light to traverse the cavity. 
     
     
       6. An oscillator as recited in claim 1 wherein said wavelength selective member forms a part of said resonant cavity. 
     
     
       7. An oscillator as recited in claim 1 wherein said wavelength selective member is a grating. 
     
     
       8. An oscillator as recited in claim 1 wherein said means for exciting said gain medium is defined by an optical pump source for generating output pulses, and wherein each output pump pulse is divided into a pair of pulses, with the first pulse in the pair defining the seed excitation pulse and the second pulse of the pair defining the primary excitation pulse. 
     
     
       9. An oscillator as recited in claim 8 wherein said excitation means further includes a partially transmissive mirror for dividing said output pump pulses into a pair of pulses, said pair of pulses travelling along two different paths to said gain medium, with difference in the length of the two paths defining the time interval between the arrival of the seed and primary pulses at the gain medium.